If you're definitely taking standard level economics, could you have a look at the notes and worksheets below:
http://www.bized.co.uk/learn/economics/markets/mechanism/interactive/part1.htm
http://www.bized.co.uk/learn/economics/qbank/markets4.htm
http://www.bized.co.uk/learn/economics/qbank/markets1.htm
http://www.bized.co.uk/educators/16-19/economics/markets/presentation/surplus.ppt
The first three things are on demand and supply. The other is on consumer / producer surplus
Have fun!
Mr W
